Parkinson's disease (PD) is a neurodegenerative movement disorder characterized by widespread neurodegeneration in the brain with profound loss of dopamine-containing neurons of the substantia nigra pars compacta. While majority of PD cases are sporadic, inherited mutations account for approximately 10% of PD cases. Existing evidence implicates a major role for stress activated protein kinases in the pathogenesis of PD. Activation of a neuronal specific c-jun N-terminal kinase-3 (JNK3), followed by recruitment to mitochondria, is associated with irreversible neurodegeneration. The mechanisms underlying this process however remain poorly understood. We have cloned a neuron-specific mitochondrial protein, called MyD88-5, which is enriched in Lewy bodies from brains of postmortem PD patients and in pathologically affected regions of the CNS in a mouse model of 1-synuclein induced PD. We showed that expression of MyD88-5 in vitro led to recruitment of JNK3 from the cytosol to mitochondria and that MyD88-5 knockout mice were resistant to dopaminergic neurodegeneration caused by parkinsonian neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). We therefore hypothesize that MyD88-5 may link JNK3 to mitochondria-dependent cell death. Three specific aims are proposed to test this hypothesis. Aim 1 will examine the role of MyD88-5 in activating JNK3 and mediating dopaminergic cell death in MPTP-induced PD using MyD88-5 knockout mice. Aim 2 will examine the role of MyD88-5 in the pathogenesis of mutant human A53T 1-synuclein-induced PD by expressing this transgene in nigral dopaminergic neurons of MyD88-5 knockout mice, or by generating and testing A53T 1- synuclein transgenic/MyD88-5-null mice. Aim 3 will dissect the role of MyD88-5 in modulating basal mitochondrial physiology and function that are important in the PD development in both MPTP- and in 1-synuclein-induced PD using MyD88-5-null mouse. Together, these studies should increase knowledge of MyD88-5-dependent cell damage pathways associated with neurodegeneration in PD and help identify new therapeutic target(s) for the treatment of PD. PUBLIC HEALTH RELEVANCE: This study propose to examine the role of a newly discovered brain mitochondrial protein, MyD88-5, in the onset and development of Parkinson's disease (PD) using the MPTP-neurotoxin and mutant human 1-synuclein mouse models. The study will enrich and refine our understanding of MyD88-5-dependent cell damage pathways observed in PD and identify new target(s) for intervention in PD pathogenesis.